A transportable neutron source is an apparatus that radiates neutrons, while being placed or moved, after it is transported near a fixed object such as a bridge, to thereby perform non-destructive inspection thereof. The neutron source is configured with a linear accelerator system for generating proton beams and a target for generating neutron beams from the accelerated proton beams.
In the linear accelerator system, the proton beams are accelerated up to an energy of about 4 to 10 MeV that is required for efficiently generating the neutron beams. The linear accelerator system is configured with: an ion source for generating proton beams; a pre-accelerator for clustering and pre-accelerating the proton beams generated from the ion source; a post-accelerator for accelerating the beams up to the energy at which neutron beams are efficiently generated; and an amplifier for feeding beam accelerating power to the respective accelerators.
With respect to transportable linear accelerator systems, they are required to be transportable by use of an ordinary vehicle. In order to make the system transportable, such an on-board configuration of a linear accelerator system is disclosed in, for example, Patent Document 1, that is a compact apparatus but is capable of causing acceleration with a large current, and that comprises an ion source, a radio frequency quadrupole accelerator (Radio Frequency Quadrupole Linac; RFQ) and a drift tube accelerator (Drift Tube Linac; DTL).
However, in the conventional transportable linear accelerator systems, a copper material is used for the radio frequency quadrupole accelerator and the drift tube accelerator serving as the pre-accelerator and the post-accelerator, respectively, in order to enhance power efficiency. Thus, when the proton beams accelerated up to an energy of about 4 to 10 MeV hit an electrode in the above accelerators, neutrons are generated, so that a thick concrete is required to prevent the neutron from leaking out of the vehicle, making it difficult to reduce the total weight as a transportable system.
In this respect, such a technique is disclosed in, for example, Patent Document 2, that makes it possible to reduce radioactivity by applying gold or aluminum on an ion beam-facing inner surface or the like, of the quadrupole electromagnet or the drift tube electrodes in the accelerators.